Transmitter for self-synchronous systems



Oct. 26, 1948. J. L. EVERETT EIAL 2,452,042

TRANSMITTER FOR SELF-SYNCHRONOUS SYSTEMS Filed Sept. 10, 1945 2 Sheets-Sheet 2 22 I 7 f E o 2o 1 J 5- 4' A 18' J ELECTRICAL 23 INPUT 3 1 7F A-sMITTER Rscg vEk June/whee I-IUHN L- EVERETT ARNOLD RAIMEE Patented Oct. 26, 1948 TRANSMITTER FOR SELF-SYNCHRONOUS SYSTEMS John L. Everett and Arnold Raines,

Philadelphia, Pa.

Application September 10, 1945, Serial No. 615,482 6 Claims. (Cl. 177380)' (Granted under the act of March '3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes. without the payment to us of any royalty thereon.

Our invention relates to electrical systems for repeating angular positions at distant points and it has special reference to position transmitting systems of the self-synchronous type.

Broadly stated, the object of our invention is to increase the accuracy and otherwise improve the performance of such systems.

A more specific object is to eliminate "from such systems a sixth harmonic error characteristic of resistor type transmitterdesigns known to the prior art.

Another object is to provide a resistor type transmitter that introduces substantially no angular error when used with system receivers of the magnetic or other conventional type.

In practicing our invention we attain the foregoing and other objects by designing the resistor type transmitter in the shape of an equilateral triangle and placing similar and uniform windings on the three triangle legs. This unique design causes the transmitter output voltages to vary in accordance with a desired non-linear trigonometric function of the transmitter rotor position and thereby enables conventional magnetic type receivers accurately to repeat the transmitter position without being subject to the sixth harmonic errors which characterize resistor type transmitters of circular contour.

One preferred form of our improved transmitter is shown by the accompanying drawings wherein:

Fig. 1 represents the new transmitter interconnected with a self-synchronous receiver of con ventional direct current magnetic type;

Fig. 2 shows one satisfactory triangular winding support structure which may be utilized by the transmitter of Fig. 1;

Fig. 3- graphically represents one typical sixth harmonic angular error which the improved transmitter design of our invention eliminates;

Fig. 4 typifies prior art constructions on the basis of which mathematical analysis of the named error can be made;

Fig. 5 represents our new system in "equivalent electrical circuit form; and

Fig. 6 is explanatory of how error elimination is achieved by going from the conventional circular winding arrangement of the prior art to the unique triangular Winding arrangement of our invention Systems to be benefited by our invention of benefiting. In the illustrative form shown this self-synchronous system is operable by direct current and includes: (a) our improved transmitter shown at the left of the diagram; and (b) a cooperating receiver of conventional magnetic type shown at the diagrams right.

Direct current voltage E for energizing the system is supplied from any suitable source of power here designated by the terminals "plus and "minus. These terminals are identified with circuit conductors 4 and 5 between which it will be assumed that I! volts or other commercially available (as from storage batteries or the like) value of unidirectional potential is continuously maintained.

The transmitters three output terminals i- 23 are interconnected with corresponding terminals l'-2'-3' of the receiver through the conventional three conductors 1B9 which span the distance between transmitter and receiver in the complete position-repeatin installation.

portion of the complete system comprises a stator structure represented as a magnetic ring I 0; three windings |l-l2l3 carried by this stator and to by an equivalent salient pole delta connected with terminals i'-2'3; and a rotor II represented as a permanent magnet with opposing end poles designated N" (for north) and 5" (for south).

As the description proceeds it will become apparent that the three stator windings I I-l2l3 may also be Y connected (as shown by Fig. 4); that each of thesethree windings will typically be distributed in slots (not shown) around the stator structure according to a well-known arrangement typified by 3-phase alternatin cur--v rent motors and generators; and that the permanent magnet type of rotor I! may be replaced armature structure magnetized by a direct current exciting winding (not shown).

This rotor I is pivotally mounted for free rotation through 360", and in operation of the complete system the angular position assumed by the rotor is determined by the direct current energizing voltages which stator input terminals 2'-3 receive from system conductors 1-8-9.

More than one of the receivers of Fig. 1 (or equivalent) obviously may be supplied from a single resistor-type transmitter (left of Fig. 1) of our improved triangular design. The receiver construction just described is, moreover, intended to typify all forms of apparatus into which the transmitter output voltages may feed. One alternative voltage receiver is shown at the right of Fig. 4; another takes the form of a "synchronous difierentia (not shown) still another takes the form of a synchronous transformer '(also not shown).

Our improved resistor t me transmitter The three receiver voltages just mentioned are derived from corresponding terminals l--23 oi the transmitter shown at the left of Fig. 1. This transmitter is of the resistor type, and in accordance with the invention is in the form of a support, or section of equilateral triangular tubing as shown at Fig. 1. The three sides of the support are identical and may be formed from any suitable sheet material having the necessary strength and durability.

Carried by the three stator sides forming the triangular structure shown at M are electrical windings l6|1-i8. In number of turns, spacing and resistance all three windings are duplieates and may satisfactorily utilize insulated wire of copper or other commercially available metal. Preferably the turns of the windings lie in respective planes substantially normal to the corresponding sides of the triangular cylinder and parallel to the central axis thereof, When such insulated wire is used, one exposed edge of all individual turns must have the insulation removed therefrom in order to permit electrical contact by brushes and 2| carried by the rotor portion 22 of the transmitter.

In one satisfactory construction this rotor element 22 may be made of insulating material and carry the brushes 2t-2l on the underside thereof. Each of these brushes has the elongated shape shown and is so mounted on the rotor as to maintain continuous contact with the particular pair of windings l6iil8 therebeneath for all rotative positions of member 22. Well known resilient means (not shown) hold the two brushes 20-2! in this desired contacting relation at all times.

From the diagram it will be seen that rotor brushes 2ll-2l are insulated from each other and respectively connected to the direct current power source leads 4-5. These two brushes are angularly spaced 180 from each other, and by reason of the connections'named they serve to impress upon the contacted winding turns immediately therebeneath the full potential E of the direct current input circuit 3 5.

Operation of complete self-synchronous system When (organized as shown in Fig. l, angular motion imparted to the transmitter rotor 22 will accurately be repeated by the receiver rotor l5 because each angular position of transmitter rotor 22 eifects a corresponding voltage apportionment between stator output terminals l-2, 2-3, 3-l;

which, when impressed upon the interconnected terminals l'2', 2'--3? and 3'l' of the receiver stator induces therein a resultant field corresponding in rotational position to the instantaneous position of rotor 22.

In this manner changes in angular position on the part of transmitter rotor 22 are accurately repeated by corresponding changes in the rotative position of receiver rotor l5. In the apparatus shown, the N end of receiver rotor I5 positionally matches with the positive brush 2!) of transmitter rotor 22; while the 8" end of the receiver rotor similarly synchronizes with the transmitter rotors negative brush 2i. In consequence all rotative motions by transmitter pointer t are accurately repeated by receiver pointer r, making receiver angle Bequal to transmitter angle A at all times.

Performance of magnetic type receivers As just indicated, the Fig. 1 receiver functions to position rotor IS in accordance with the voltages impressed upon the receivers stator windings H-l2-l3. The operational details of such p0- sitioning may be preliminarily analyzed as follows.

The currents flowing in windings lll2l3 produce magnetic fields each of whose directions is along the axis of the coil in which the fieldproducing current flows, These three magnetic fields thus are 120 apart in spacing, and their magnitudes vary in the same way as do the fieldproduclng currents. The resultant of these three fields obtained by a vectorial addition determines the direction along which rotor l5 will come to equilibrium.

By proper variation of these three currents the rotor it: may be made to assume any direction desired. The range of such possible positioning includes the full 360 rotative travel, and by reason of the magnetically polarized character of the rotor each distinctive set of stator energizing voltages will correspond to one and only one equilibrium rotative position of the rotor.

Receiving apparatus functioning in the manner just described is well known to the art; one alternative arrangement thereof is shown at the right of Fig. 4; other forms include synchronous differentials and synchronous transformers (not shown) and our improved synchronous transmission system contemplates use of any and all of such receivers in the form as they existed prior I to our transmitter improvements herein disclosed.

Resistor type transmitters of the prior art Until the advent of our invention the only resistor type of transmitter known to us as available for use with the just described receiver apparatus employed three windings (corresponding to 56-47-58 of Fig. 1) mechanically supported on a member shaped as a circular ring. In Fig. 4 such a circular ring is represented as carrying windings i6-ll'l8'. Winding interconnections as shown by Fig. 4 were utilized together with diametrically opposed brushes through which a direct current voltage was applied between the opposed contact points on one edge of the windings.

With this circular winding support arrangement it was found that the desired accurate positional correspondence did not exist between the transmitter rotor 22 and the receiver rotor l5. Instead, errors of the type dlagrammed by curve 24 of Fig. 3 were found always to be present.

Fig. 3s curve 24 (full line) is based on actual test results obtained with a system made up monic swam of the conventional magnetic type rcceiver diatriangular support H evolved by us. From Fig.

3 (curve 24) it will be seen that the exact positional matching between receiver rotor II and transmitter rotor 22 occurs only at substantially 30 intervals.

Between these intervals the receiver rotor (pointer r) is either ahead of or behind the transmitter rotor (pointer t) and this produces the represented error curve 24 with sixth harcharacteristics. While the magnitude of the error indicated is only of the order of two or three degrees, yet many applications of position repeating systems require higher accuracy and cannot tolerate this substantial departure from accurate positional coincidence.

In the past such high accuracy requirements have required use of self-synchronous systems incorporating conventional non-resistor type alternating current transmitters where the maximum positional error can easily be kept below four-tenths of a degree. Applying this limit to the devices of Fig. 1, the receiver pointer r must at no time be out of phase with the transmitter pointer t by more than four-tenths of one degree. This means that the receivers reference angle B must at all times match the transmittersreference angle A within the named limits.

Direct current and other synchronous systems using the resistor-type prior art circular transmitter of Fig. 4 obviously cannot meet such rigid requirements, for in them. as Fig. 3s curve 24 shows, the receiver .reference angle B is at times less than the transmitter reference angle A by nearly two degrees and at times greater than the transmitter reference angle by nearly the same amount. The total spread is therefore of the order of between three and four degrees as compared with the eight-tenths degree requirement (total) which must be met in remote fire arm positioning and certain, other applications.

Inherent nature of the circular transmitter error ments show and reference to Fig. 6 will confirm that such. transmitters (typified by circle 23) ter pointer t. All conventional designs of m netic type receivers are, moreover, found to exhibit this same characteristic and hence none of them can with complete satisfaction be used in conjunction with resistor type transmitters of the prior art circular form.

Accuracy characteristics of our triangular transmitter Investigation conducted by us has revealed that by a proper alteration in the geometrical pattern of the transmitter winding support there may be provided transmitter output voltages which so relate themselves to transmitter reference angle A that when applied to conventional receivers the desired coincidence of receiver rotor following will be achieved to almost any degree of accuracy desired (within the limits of mechanical tolerance factors). Since these limits are well below the four-tenths degree error requirement for conventional alternating current self-synchronous systems, we have thus enabled direct current systems so to improve their accuracy as to perform on a par with the alternating current organizations. 7

Extensive mathematical studies plus other analyses made by us have shown that this desired relationship for sixth harmonic error elimination is achieved when the three transmitter windings i6-l'li8 are supported in the equilateral triangular relationship shown generally by Fig. l and at H by Fig. 2. This triangular. shape for the winding supporting structure l4 results in transmitter output voltages which vary according to a nonlinear trigonometric function of the rotor reference angle A.

There has been obtained by us experimentally (and also analytically, as later set forth) a def-. inite non-linear trigonometric function shown to be that which conventional magnetic type receivers require to effect an accurately synchronous following of all angular movements of the transmitter rotor. Our triangular winding support improvement which gives this function is, in

fact, found totally to eliminate the sixth harmonic error curve 24 shown by Fig. 3 as typifying circular winding transmitters of the prior art.

Instead the error curve which is typical of our improved system has the relatively flat shape illustrated at 25 (dotted curve) by Fig. 3 andshows position-matching departures introduced by mechanical factors only. We find that this curve 25 can readily be made to fall well within the generate output voltages (between terminals l2, 2-3, and 3-0 which var as a linear function of the transmitter rotor 22's angular position. As here used the term "linear refers to a straight line variational relationship between the transmitter output voltages (open circuit measurement) and the transmitter rotors position angle A.

Synchronous receivers of the conventional magnetic type shown by Fig. l are, however, found four-tenths degree permissible error limit earlier discussed. Comparison with the sixth harmonic 1 error curve 24 shows that the improvement represented-is substantial, and that by reason thereof direct current self-synchronous systems have now been given accuracies fully competitive with conventional alternating current systems.

Mathematical verification For mathematical verification of the foregoing the following analysis is presented. This analysis shows: (a) that linear transmitter windings on a circular supporting structure result in a transmission system having the inherent sixth harmonic error earlier referred to; and (b) that our novel triangular" form of transmit er winding support totally eliminates this error without introduction of substitute inaccuracies.

Consider first the general form of transmitter shown at the left of Fig. 4. Each of its three windings l2, 2-3, 3l (l6l|'-i8') is identical'to the othertwo. No other restrictions as to shape of winding support or uniformity are here placed. Under these general conditions let:

T designate the total ohmic resistance of each of the three transmitter windings l2, 2-3, 3-l (l6'-i|-l8') as measured between end terminals (with the winding disconnected from the other circuit parts) A designate the angle (expressed in degrees) between transmitter terminal I and the point of contact of rotor brush 20 with winding l-J.

Then:

I(A)T designates the resistance of that portion of winding |'-3 between terminal I and contact 20 therewith when that contact is displaced from point I by angle A. In the foregoing expression, j(A) is an arbitrary function which describes the geometrical configuration and other features of the winding 3-4.

Consider next the general form of receiver shown at the right of Fig. 4. For convenience of analysis the represented Y connection of the three receiver input windings will be assumed. The angular position of the receiver rotor I5 is measured in a clockwise direction from the axis of winding l'. In Fig. 4, this angle of receiver rotor position is designated by B, which like transmitter rotor angle A also will be expressed in degrees.

Let the rotor 20-2I of the Fig. 4 transmitter be energized by a voltage E. In consequence there will appear between transmitter terminals i--2--3 output potentials which flow currents through the three receiver windings. Let these currents be designated as 11 for winding 0-| i: for winding 0-2 3 for winding 0-3 In a receiver of the general type here considered, the magnetically polarized rotor I5 will be in equilibrium at the angle B if the following condition is satisfied:

ii sine B-l-iz sine (B+120) +i3 sine B+24o =0 (1) Under this condition the rotor I5 is aligned with the resultant magnetic field which the three named receiver winding currents jointly produce.

In order for the transmitter-receiver system to be accurate, receiver angle B must at all times equal transmitter angle A. Therefore, for the receiver rotor accurately to reproduce the position of the transmitter rotor, it is necessary that for all values of A the construction of the transmitter be such that:

ii sine A+i2 sine (A+120) +i3 sine (A+240) =0 (2) tangent A and either terminal thereof.

This is because variation in transmitter winding This equivalent circuit of Fig. 5 is valid only in the range of A=0 to A=60. Were, however, equivalent circuits to be set up for other angular ranges,'it would be found from them that the conclusions presently to be derived apply for the entire 360range of rotation of the transmitter rotor.

, This is due to the 60 related symmetry which the Fig. 4 transmitter possesses.

By use of the Fig. 5 circuit and Kirchhois laws the three receiver winding currents i1-1a-i3 may be computed. Substituting such computations in Equation 3 above results in the condition for f (A) which is:

f( t6 )+f( V f( Neither T nor R appears in this equation, indicatingltherefore that the absolute resistances of the two units (transmitter and receiver) do not aflect the error.

For the case of linear windings on the "circular cylindrical supports of the prior art.

tangent A resistance is directly proportional to the included winding angle. Substitution of this into Equation 4 results in It may be shown that with such linear windings A on circular supports this Equation 5 is satisfied only when A=0 or 30 or 60, and is not satisfied for any other values of A in this range. It may further be shown that throughout this 0 to 60 rangethe attendant error passes through a, complete cycle of the general character represented at 24 by Fig. 3, and that the same cyclic error repeats itself for each other corresponding range (60 to 120 to 180 to 240; 240 to 300; 300 to 360) of transmitter rotor positionins.

From the foregoing it may b concluded that uniform transmitter winding on a cylindrical support of the circular cross section represented by Fig. 4 will produce a sixth harmonic error of the cyclic variety just described. In shapev the cal-' culated error graph will be similar to the well known sine curve. One set of experimental observations gave curve 24 of Fig. 3 (earlier described).

To find for f (A) the function which will elimihate the sixth harmonic error just described, it is necessary to proceed by the trial and error method in searching for the )(A) which will satisfy Equation 4 at all transmitter angular posi tionings between A=0 and A=60. Using suc trial and error substitution procedure we have discovered that when:

tangent A= tan A .sulated wire uniform both as to size and Equation 4 will be so satisfied for all values of A in the to 60 range stated.

.The above Equation 6 specifies a variation in resistance which the triangular" transmitter of.

distance to be:

tan A 1+ /:T'tsn A' where M=the distance from center of Fig. 6 triangle l-Z-S to any one 01' that triangles vertices (as indicated).

Comparison of the function Just stated with Equation 6 shows complete identity except for the constant of proportionality. That constant depends upon the total resistance of the winding between I and 3; it was previously indicated, moreover, that the error underdiscussion was completely independent of that total resistance.

Therefore that portion of the Fig. 1 winding l8 between terminal I and brush contact for A=60 will produce an errorless system. By symmetry, all other corresponding sections of the complete triangle l-2-3 will likewise produce the same 'errorlcss result. 7

Hence, use of our triangular winding support design will give a system without inherent errors over the entire 860 range of rotation of the transmitter rotor.

Practical advantages of our improved construction A transmitter having the improved triangular construction shown by Fig. 1 and just described oil'ers many practical advantages. Such a. triangular design has been found by us to aiIord the most convenient means of eliminating the sixth harmonic error (curve 24 of Fig. 2). It permits use of three exactly similar windings |6- 11-? which have uniformly spaced turns of ininsulation thickness and each turn of which may duplicate all other turns in included length and resistivity,

Cusping or other special alteration of the winding support structure I! (see Fig. 2) thus is not necessary and insulated winding conductor of uniform size and resistivity may be employed, as just stated.

In fact no special expedients other than the represented triangular shaping of the winding support need be resorted to.

The elongated winding contacts 202| of the transmitter rotor 22, moreover, offer no special problem and work performed by us indicates that same can be made just as practical and trouble free as the corresponding contacts required by circular transmitter designs of the prior art.

Summary our improved made certain rel presented herein make it clearly apparent that input voltage E may be an alternating current potential as well as a unidirectional potential. The improved transmitter design here disclosed is therefore capable of benefiting self-synchronous position transmitting systems of both the direct current and the alternating current types.

From the foregoing it will be seen that we have made highly practical improvements in position transmitting systems of the self-synchronous type; that we have increased the accuracy and otherwise improved the performance of such systems; that we have eliminated from such systems a sixth harmonic error characteristic of resistor type transmitter designs known to the prior art: and that we have provided a resistor type transmitter that introduces substantially no angular error when used with system receivers of the magnetic or other conventional type.

Our inventive improvements are therefore extensive in their adaption and hence are not to be restricted to the specific form here shown by way of illustration.

We claim:

1. In a telemetric electric transmitter, a coil support comprising a length of tubing in the cross-sectional form of an equilateral triangle in a plane normal to the central axis thereof, to form three legs, a winding on each respective leg, the common terminals of adjacent ends of successive windings being adapted for connection to respective terminals of a remote repeater, a rotor pivoted on said central axis and having arms extending oppositely from said axis, a contact on each arm each contact being adapted to make continuous electrical contact along the length of each coil in succession as said rotor is turned about said axis, each contact being adapted for connection to a respective terminal of a source of direct current potential. I

2. A transmitter for a self-synchronous electric telemetric system, said transmitter comprising a winding support in the form of an equilateral triangle, a coil on each leg of said triangle, all said coils having the same resistance per unit length along the coils, a rotor pivoted at the geometrical center of said support, said rotor having two radially extending electrically insulated arms, each said arm being adapted to make continuous electrical contact with and along said coils, in succession at points angularly spaced by for all positions of rotation of said rotor, each end of each coil being connected with the adjacent end of the next coil.

3. An electric telemetric transmitter comprising a winding core in the form 01' an equilateral triangle, a coil on each side of said core, all said coils being uniformly wound and having equal resistance per unit length along the coils, a rotor pivoted at the geometrical center of said support,

said rotor having two insulated contacts adapted to make continuous contact with said coils in succession at two points angularly spaced by 180 about said center, one end of each coil terminal being electrically connected with the adjacent end of the next succeeding coil terminal.

4. In an electric telemetric transmitter, a core in the form of an open, equilateral triangle having sides of uniform cross-section, a coil wound upon each of said sides, each said coil having the same resistance per unit length measured along said sides, each end of each coil being connectedto the adjacent end of the next succeeding coil,

a rotor pivoted upon an axis at the geometrical center of said triangle, said rotor having oppoaacaoaa sitely disposed arms each adapted to make continuous contact with said coils through 360 of rotation of said rotor, said arms being insulated one from the other, and making contact with said coils at points spaced 180 about said axis, and connections between each arm and a respective terminal of a source of potential.

5. In a self-synchronous electrical transmission system, a transmitter including in combination, three similar windings having the same resistance per unit length of coil, means supporting said coils in fixed relation to form an equilateral triangle, each coil being electrically connected ateach end with the adjacent end of the next succeeding coil, a rotor pivoted upon an axis passing through the geometrical center of saidvtriangle, said rotor including contact arms insulated from each other, each arm making contact with said coils successively throughout 360 vof rotation of said rotor, the point of contact of each arm with said coils being spaced 180 from the point of contact of the other arm, whereby the total resistance of a coil from a predetermined connection between adjacent coils to the point of contact of the arm with said coil is proportional to I 2 tan 3 a 1+1/ tan 0 where 0 is the angle between the radials from said axis to said connection and said point.

JOHN L. EVERETT. ARNOLD RAINES.

aarmmwns crran The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,197,636 Faus Apr. 16, 1940 2,316,987 Pittet Apr. 20,-1943 Borsum Mar. 12, 1946 OTHER REFERENCES Pages 104-105 of Instruments," vol. 10, April 1937. 

